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Avalanche Forecast

Archived

Jan 11th, 2023–Jan 12th, 2023

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Purcells, Dogtooth, East Purcell, West Purcell.

Make conservative terrain choices and think about the consequences of being wrong. Small avalanches can step down to deeper layers resulting in large and dangerous avalanches.

In General the snowpack is weak and there is an ongoing risk of triggering a deep persistent slab. Stay away from steep, shallow and rocky terrain features.

Confidence

Moderate

Avalanche Summary

On Monday evening we received reports of a fatal avalanche accident. This Avalanche occurred on a west facing slope at treeline in the southern Selkirk mountains. This avalanche did not occurre in this forecast region but similar snowpack conditions exist in the Purcells. This MIN report has more details.

On Tuesday a few small wind slab avalanches were observed in northfacing alpine.

Please continue to share any observations or photos on the Mountain Information Network.

Snowpack Summary

Wind effected surfaces exist on exposed treeline and alpine features. A new surface hoar layer can be found just below the surface as well as a crust on some steep south facing slopes.

The upper snowpack continues to settle. The mid and lower snowpack is generally weak and faceted, with a number of weak layers. Of significant concern is a layer down 30 to 50 cm from the surface consisting of a crust, facets, and/or surface hoar. And a layer of large facets and a crust down roughly 50 to 110 cm from the surface. The snow below this deeper weak layer is unconsolidated and weak.

Snowpack depths remain highly variable, ranging from 60 to 150 cm at treeline. In General the snowpack is shallow and weak.

Weather Summary

Wednesday Night

Cloudy with the possibility light flurries bringing trace amounts of new snow. Light to moderate southerly winds and a low of -13 at 2000m.

Thursday

Cloudy with flurries bringing a few centimeters of new snow. Strong southerly winds and a high of -3 at 2000m.

Friday

Stormy with up to 10cm of new snow expected at treeline and above. Rain at lower elevations. Warm air aloft with temperatures around 0 at 2000m. Moderate to strong southerly winds.

Saturday

Cloudy with flurries bringing around 5cm of new snow. Light southerly winds and a high of -3 at 2000m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Uncertainty is best managed through conservative terrain choices at this time.
  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • Be mindful that deep instabilities are still present and have produced recent large avalanches.
  • Be especially cautious as you transition into wind affected terrain.

Problems

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.